Disappearing render files

I'm seeing an occasional strange problem with my rendered clips (typically nested sequences). I open a sequence I've created with some previously rendered clips. I play it through and everything works fine. Then I switch to another application such as iPhoto, and when I switch back to FCP many of the clips have the red bar above them and have to be re-rendered. If I close the file without saving and re-open it, the rendered versions come back (red bars are gone and I can play the clips), but again if I switch to another application and switch back to FCP, the clips become unrendered again. This doesn't affect all of the clips in the sequence, only some of them.

Also, sometimes when I open a FCP file for the first time after starting up my computer, some of the clips are not rendered, even though I'd rendered them previously and watched them just the day before.

Any idea what's going on here?

thanks,
Scott

Message was edited by: Scott Stark

Message was edited by: Scott Stark